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As surely as waves of ripening wheat, blue-green algae warnings have become perennial harbingers of summer for the county.

Three consecutive weeks of warnings for Marion Reservoir have affected the county’s largest tourism draw.

“It has decreased visitation numbers,” Corps of Engineers office manager Torey Hett said. “We have the swimming areas closed. Boat ramps are still open because it’s still OK to go fishing in blue-green algae as long as you wash your hands well and eat just the filets.”

Cyanobacteria, the scientific name for blue-green algae, are normally present in lake and pond water in small amounts that don’t pose a threat.

However, during hazardous algal blooms, more than 30 varieties can produce toxins that affect human and animal health. Some toxins cause mild skin irritations, while others can cause serious liver and nervous system damage. Humans and animals have died from ingesting excess toxins from several varieties.

It’s impossible to know exactly what toxins are present in a given bloom without extensive laboratory testing.

The reservoir is tested weekly, but the county lake is tested only when lake superintendent Steve Hudson suspects a problem.

“We don’t have any problem at this time,” he said. “The only time I’ve seen it was when we had those big flooding rains earlier this year. I think a lot of it had to do with residents’ fertilizer on their grass. We had a short bloom then. Once the water dropped, it dried out along the shore line.”

When Hudson has a concern, he collects water samples in jars and lets them “sit for a few hours” for algae and sediments to separate.

“We send photos or pictures of that to KDHE, and they determine if we have it,” Hudson said. “In the past, they’ve come out and done samples themselves.”

“Any time we’ve got hot weather like this it’s a concern,” he said. “It’s hard to tell just looking. The really obvious ones look like green paint in the water.”

Cattle dying from consuming blue-green algae is “theoretically possible,” Kraus said, although they rarely show signs of illness.

Dogs that drink contaminated water or eat dried algae may become lethargic, display vomiting or diarrhea, and develop jaundice and abnormal swelling.

Farmers sometimes bring water samples for Kraus to inspect, and they can work with veterinarians or county extension to have samples tested by Kansas State University.

Kraus recommended checking ponds weekly during hot weather.

“With the prevailing south winds, it would be more likely to be on the north shore,” he said.

Runoff from agricultural production is a major source of nutrients for blue-green algae.

The tactic Marion Watershed Restoration and Protection Strategy has pursued for 12 years to battle blue-green algae at the reservoir is straightforward but daunting: Eliminate its food; kill the algae.

Stemming the flow of phosphorous — about 76,000 pounds per year — has been a primary objective.

“Our focus has changed in the last three years from being scattered over the 200 square miles of the watershed to focusing on specific target areas for implementation of best management practices,” WRAPS coordinator Peggy Blackman said. “We have decreased nutrients going into the reservoir. Our phosphorous goal is 70 percent reduction, and we’re not anywhere near that goal.”

Among seven strategies designed to reduce contamination from cropland erosion, planting no-till cover crops is the most promising, Blackman said. No-till farming is 3.5 times more effective than terraces.

Two producers have enrolled 533 acres in a cost-sharing no-till management program funded by WRAPS, but many more farmers in the watershed have adopted the practice, Blackman said.

Counting the value of contributions from WRAPS participants and collaborators, the project has parlayed $1.3 million of grants into about $2.3 million devoted to tackling the algae problem. The project was recently funded for three more years.

However, WRAPS can’t do anything about phosphorous-laced sediment that flowed into the lake before WRAPS’s inception. Even if the project were to hit its reduction targets, blue-green algae blooms could be around for years, Blackman said.

“Anything that flowed into the reservoir prior to 2003, those nutrients are in the sediment,” she said. “Until those nutrients that have been there since 1964 have been utilized, we’ll continue to have blue-green algae.”

Creating vegetative buffers that filter runoff and working with nearby livestock owners has had positive effects at the county lake.

“One problem was cattle droppings,” Hudson said. “We got with the landowners and they participated in building a fence that keeps cattle from getting too close to the water.”

A mild winter helped to reduce another animal-source contaminant.

“We didn’t have nearly the population of geese this past winter,” Hudson said.